The present invention relates to oxides-enclosed fine glass particles in each of which fine particles comprising oxides and salts are enclosed, and to a method of manufacturing the same.
Conventionally, mixed particles, in which particles of a mother material are mixed with fine particles of auxiliary agents or additives such as oxides and salts, or a mixture of the mixed particles with binders, are used in the field of mechanical components having high hardness and high accuracy such as cutting tools, dies, and bearings; in the field of materials used for, for example, engine valves which require the resistance to wear and abrasion at a high temperature; in the field of functional materials such as capacitors and sensors; and in the field of electric insulating materials used for, for example, various types of electric insulating parts
When, for example, a sintered body is produced, particles of a sintering mother material are mixed with fine particles of oxides and salts that act as sintering auxiliary agents and with fine g ass particles, and further mixed with binders when necessary, thereby obtaining a mixture thereof. Then, a green body is obtained by molding the thus obtained mixture in a predetermined shape, and the resultant green body is sintered at a given temperature under a given pressure,
It is preferable here to uniformly scatter fine sintering auxiliary agents in an amount as small as possible. However, it is more difficult to uniformly scatter fine sintering auxiliary agents in a small amount and to mix them with particles of a sintering mother material because the fine sintering auxiliary agents are more liable to agglomerate.
To cope with this problem, there are manufactured coated particles in such a manner that particles of a sintering material such as particles of inorganic materials including diamond particles and ceramics particles, and metal particles are used as core particles, and the core particles are previously coated evenly and uniformly with various types of metal materials and inorganic materials such as ceramics, oxides, carbides and nitrides that act as the sintering auxiliary agent.
These coated particles are used to improve the bonding strength and the denseness between different types of ceramics and between different types of metals in sintered bodies and thermally sprayed parts.
Unexamined Japanese Patent Application Publication JP 3-75302 A, and JP 7-53268 A to JP 7-54008 A filed by the present applicant, for example, disclose coated particles comprising particles of an inorganic material or a metal material having an average particle size of 0.1 xcexcm-100 xcexcm, each of the particles being covered with superfine particles of the same type or a different type of an inorganic material or a meal material each having an average particle size of 0.005 xcexcm-0.5 xcexcm, and also disclose a method of manufacturing the coated particles the method of manufacturing the coated particles disclosed in these publications, after superfine particles are created by a vapor-phase method such as a thermal plasma method, core particles to be covered are introduced into the flow of the thus created superfine particles or into a space in which the superfine particles are created; and both the superfine particles and the core particles are caused to come into contact with one another in a flowing state; and thereby the surface of each core particle is covered with the superfine particles.
While the coated particles disclosed in these publications are useful in the manufacture of sintered bodies, it is difficult to obtain coated particles each of which is simultaneously covered with fine particles of a plurality of types of sintering auxiliary agents.
Accordingly, there is required a method of evenly and uniformly mixing the particles of a sintering mother material with a small amount of fine particles of a plurality of types of sintering auxiliary agents, optionally or when necessary.
Incidentally, fine particles, and in particular, fine particles of oxides and salts having a particle size of 1 xcexcm or less are widely used as an auxiliary agent such as a sintering auxiliary agent or as an additive, as described above. However, the auxiliary agent and the additive exert their performance by their nature when they have a particle size smaller than that of a mother material and are contained in the mother material in a small amount Thus, fine particles used for this application must be evenly and uniformly mixed with the mother material in a well scattered state without agglomerating in the mother material.
For this purpose, conventionally, when a plurality of types of oxide powders are mixed with a mother material powder, each oxide powder is made as fine as possible and mechanically mixed with the mother material powder so as to keep the oxide powder in a highly scattered state. However, since a fine oxide powder has a stronger agglomerating force, even if the powder is mixed with a mother material powder macroscopically, a multiplicity of agglomerated powder composed of a single component is scattered microscopically. As a result, there arises a problem that an ideally scattered state cannot be obtained. Further, it is very difficult to scatter each of the agglomerated bodies of the oxide powder that have agglomerated once in a mixture by pulverization or grinding.
The fine particles of the auxiliary agent powder are liable to agglomerate in a state as they are, and moreover they are added in a small amount in many cases, as described above. Thus, when the fine particles of the auxiliary agent powder are only simply mixed with the particles of the mother material powder, they are unevenly distributed. Accordingly, it is difficult to evenly distribute the fine particles of the auxiliary agent powder in the mother material powder for uniform mixing.
Accordingly, when particles of a mother material powder are mixed with a small amount of fine particles of an auxiliary agent powder, there is eagerly required a method and an apparatus for not unevenly distributing but evenly scattering the small amount of the fine particles of the auxiliary agent powder for uniform mixing.
A first object of the present invention is to solve the problem of the above conventional technology by providing oxides-enclosed fine glass particles from which highly scattered fine particles of oxides can be easily obtained and in which a plurality of kinds of fine particles of oxides can be evenly and uniformly mixed with a small amount of a mother material without being scattered unevenly.
A second object of the present invention is to provide a method of manufacturing oxides-enclosed fine glass particles capable of easily manufacturing the novel oxides-enclosed fine glass particles.
As a result of diligent studies performed by the inventors for solving the above problems, the inventors have found that highly scattered fine particles of oxides can be easily obtained by preliminarily making fine particles in each of which oxides are enclosed in such a manner that a plurality of pieces of fine particles of oxides are scattered and enclosed in each of fine glass particles acting similarly as an auxiliary agent, and by pulverizing the thus obtained oxides-enclosed fine glass particles when necessary, contrary to a conventional technical common knowledge that a powder material of oxides is pulverized and mechanically mixed with a powder mother material; that even if fine particles of oxides are mixed with a mother material, they can be evenly and uniformly scattered therein without being agglomerated and without being unevenly scattered; and that glass is most suitable as a material in which the fine particles of oxides are enclosed because the glass improves the scattering property of fine particles themselves in which oxides are enclosed. Accordingly, the present invention has been completed based on the above knowledge.
That is, oxides-enclosed fine glass particles, characterized in that two or more pieces of at least two kinds of enclosing particles, which comprise oxides, double oxides, or salts of oxyacids, or double oxides or double salts thereof, are enclosed in each of fine glass particles.
It is preferable that an average particle size of the fine glass particles is 0.05-1 xcexcm, and the average particle size of the enclosing fine particles is 0.01 xcexcm-0.3 xcexcm and less than one half of the average particle size of the fine glass particles.
It is preferable that the oxides, double oxides, or salts of oxyacids, or double oxides or double salts thereof, which constitute the enclosing fine particles, are at least two members selected from the group consisting of titanium oxide, zirconium oxide, calcium oxide, silicon oxide, aluminum oxide, silver oxide, iron oxide, magnesium oxide, manganese oxide, yttrium oxide, cerium oxide, samarium oxide, beryllium oxide, chromium oxide, barium oxide, vanadium oxide, barium titanate, lead titanate, lead titanate zirconate, lithium aluminate, yttrium vanadate, calcium phosphate, calcium zirconate, iron titanium oxide, cobalt titanium oxide, and barium stannate.
Further, a method of manufacturing oxides-enclosed fine glass particles according to a second aspect of the present invention is characterized by comprising the steps of mixing a powder material of glass with a powder material of oxides which comprises oxides, double oxides, or salts of oxyacids, or double oxides or double salts thereof that are not made to glass; converting the thus obtained mixture of the powder materials into a mixture in a vapor-state by supplying thermal plasma to the powder materials; and quickly cooling the mixture in the vapor-state, thereby manufacturing oxides-enclosed fine glass particles in each of which two or more pieces of at least two kinds of enclosing particles, which comprise oxides, double oxides, or salts of oxyacids, or double oxides or double salts thereof, are enclosed.
It is preferable that an average particle size of the fine glass particles be 0.05-1 xcexcm and that the average particle size of the enclosing fine particles be 0.01 xcexcm-0.3 xcexcm and less than one half of the average particle size of the fine glass particles.
It is preferable that the oxides, double oxides, or salts of oxyacids, or double oxides or double salts thereof, which constitute the powder material of oxides are at least two members selected from the group consisting of titanium oxide, zirconium oxide, calcium oxide, silicon oxide, aluminum oxide, silver oxide, iron oxide, magnesium oxide, manganese oxide, yttrium oxide, cerium oxide, samarium oxide, beryllium oxide, barium titanate, lead titanate, lead titanate zirconate, lithium aluminate, yttrium vanadate, calcium phosphate, calcium zirconate, iron titanium oxide, cobalt titanium oxide, barium stannate, chromium oxide, barium oxide, and vanadium oxide.
It is preferable that an average particle size of the powder material of glass is 0.5 xcexcm-10 xcexcm, and the average particle size of the powder material of oxides is 0.1 xcexcm-5 xcexcm.
It is preferable that the temperature of the thermal plasma is higher than a boiling point of the powder material of glass and the boiling point of the powder material of oxides and that an atmosphere in the thermal plasma is an atmosphere equal to or less than an atmospheric pressure.
It is preferable that the atmosphere in the thermal plasma is 25 kPa-80 kPa and that an atmosphere in which the mixture in the vapor-phase is quickly cooled is an inert atmosphere, an oxidizing atmosphere, or a reducing atmosphere.